EJ251 - Honest opinion, should I even bother with this block?

[Mad Mechanic]

Hello fellow forum members!

So I'm looking for an honest opinion on this.

Last year I pulled a used EJ251 out of a 2003 Outback that was in a self-service (Pick-n-Pull) auto yard.

I've been wanting to experience a full engine tear down and rebuild, so I pulled this motor specifically because I wanted the simplicity of the SOHC setup. I also wanted a MAP equipped motor.

I have ambitions of using this motor for...something...at some point (famous last words  ) but what I'm more thinking about now is this: is the block even worth using?

The block itself is in good shape, there is even still evidence of factory crosshatch in the cylinders. But being an EJ251, the cylinder supports are the "least desirable", just thin little bits of metal at the ends (see picture).

Now, I don't really have ambitions to turbo charge this motor, but I would like to tinker with it in N/A form (I'm a mechanical engineer by profession, it's often in my nature to tinker in the most challenging route possible).

If the consensus is that this block just isn't worth messing with, that's fine, I will turn it into a coffee table or something, but in that case, what block should I be hunting?

I really don't want to shell out for an STI shortblock, in fact whatever block I end up with I want to transfer over my good parts, like my SOHC heads.

Something else to think about is that this EJ251 block uses the oddball 131.6mm CC connecting rods, whereas later EJH25's used the more common 130.5mm CC connecting rods. Would it be worth trying to find one of those blocks? I would suspect my heads would still fit.

I am looking for constructive responses please.

[SUBIE RAT]

I have been running the 96 to 99 2.5 naturally aspirated engines for years and many long commuter miles. I have only had trouble with the 05 turbo version. I have learned to do the maintenance regularly and never ever overheat them. Because of my experience I would still use them. Just expect every hundred thousand mile to do head gaskets. At two hundred thousand be looking for a new block. My favorite mechanic Allan @ double j said never build a block with over two hundred thousand miles on it. He said it just would not be a reliable rebuild.

[Mad Mechanic]

Hello Subie Rat,

 

Your 200k miles suggestion could be an issue in my case as I have no idea how many miles are on this block. The donor car had a digital mileage indicator, so mileage already accumulated is unknown.

 

I wonder why your mechanic recommends getting a new block at 200k? I'd always heard that subarus are fiercely reliable cars with many examples racking up several hundred thousand miles on them.

[heartless]

...never build a block with over two hundred thousand miles on it...

 

that is very "old school" thinking and really does not apply here.

 

Every Subaru I have owned has gone WELL over 200,000 with few, if any, issues. the chassis' gave out before motors even thought about giving up (i live in the salt belt, rust is a killer).

 

My current car (3rd Suby, a 95 Legacy, EJ22) has about 230,000 on the odometer and still going strong.

 

The first Subaru I owned (89 GL, EA82) was still running strong, would start every time with the first twist of the ignition, and had 283K on it when it was retired due to rust issues. it was actually started and driven up on to the trailer when it was finally hauled away.

 

The second one (90 Legacy, EJ22) had 265K when it was retired - also due to rust issues. Motor ran great. In fact, the kid I sold it to for parts poured a couple of gallons of fresh gas in it after it sat for about a year, stuffed a battery in it, and it fired up with no major issues.. ran a bit rough until the fresh gas got to the cylinders, but it ran. He drove it home. (and it also had an arcing coil pak and cheap plug wires on it...I had taken the good parts off this car to put on the current one)

 

I know there are others out there that have higher mileage cars than I have had....and the greater majority with no major rebuilds...

 

sorry, Mad Mechanic - I have no personal experience with the 2.5 engines, other than the 25D, which was pretty much junk...

Edited May 24, 2016 by heartless

[Fairtax4me]

On an old cast iron block, yeah maybe 200k is a good cutoff to say it shouldn't be rebuilt.

 

On modern aluminum blocks you can rebuild them at 500k as long as the cylinders aren't too far out of round.

 

De-glaze the cylinders with a stone hone, if you don't see any low spots (places the stones didn't touch) then pop some rings and bearings in it and put it back in the car.

[Mad Mechanic]

So back to my original post topic, I'm still trying to decide if my EJ251 block is worth messing with from a structural strength standpoint. I'm sure the block itself is perfectly serviceable if someone just wanted to do a rebuild and shove it back into a daily driver, but that's not my ultimate goal with the franken-build I've got rolling around in my head.

 

I contacted a local auto-dismantler that will sell me an EJ255 non-turbo shortblock for $1300, I would then use this shortblock with my SOHC heads and EJ251 MAP intake manifold. Might seem a bit backwards, but as I said I like the design and serviceability factor of SOHC setups.

 

$1300 seems a bit steep to me honestly, considering I pulled my entire complete EJ251 with full engine harness and ECM from a local Pick-n-Pull yard for around $350.

 

So, thoughts on my original post topic?

[Fairtax4me]

Unless you're running a turbo I really wouldn't worry about the strength of the block. 

People build franken-motors with the 251 and 253 blocks with early 2.2 heads on them and have no problems with reliability running around 10.5-11:1 compression. 

 

This is the general build for people looking for mid range and low rpm torque. 

 

If you're looking for power at high revs, the SOHC heads arent really the way to go. No doubt there are some things that can be done to improve them, such as porting and oversized valves, but the same can be done to the DOHC heads and get better improvement still. 

[Mad Mechanic]

More than anything I'm interested in tinkering with the potential of the 251 in SOHC N/A form. I'd like to extract a little more power than the 165 rated HP and 167 lb-ft torque. How much more I don't know, I've read accounts of people spending crazy amounts of money trying to get power near stock WRX turbo motors (some claims more credible than others).

 

Not looking for high RPM power, looking more for power at normal driving revs, the "fun zone". I'm probably going about this the wrong way and if I really want to mess with an N/A motor I should probably look for a 254 DOHC, but this was the motor I chose to start with.

[WoodsWagon]

The block is the part least worth worrying about. If you're going to beat on the engine, the rod bearings are always the first thing to go. Put your efforts toward oiling, rods, and bearings. The n/a 2.5l blocks don't split cylinders until more than 20psi of boost goes through them.

 

Plenty of power to be made with a tunable ECU. The VW sandrail guys pull a fair bit more out of the stock subaru engine with an aftermarket EMS.

Edited May 25, 2016 by WoodsWagon

[idosubaru]

Use it, NA power is small change and not going to touch the block. you're not going to hit 200+ hp which is chump change for the block.  as he said - look into bearings and oiling, that's where those engines fail, and don't run it hot.

[kamesama980]

Unfortunately there's limited gains to NA hp in the "usable" range. I'm in the same mindset about usable vs peak power. you can get a better low-mid rpm torque cam but it won't improve the number of HP, just bolster the midrange a little. Since you're limited to ~100% VE (think of it as limiting how much torque you can gain) with an NA, the biggest hp gains come from increasing the revs. the same torque at higher rpm = more power. so a 200+hp 2 or 2.5l doesn't make any more power in the daily driver rev-range, it makes it at 8k rpm, usually sacrificing low end.

 

Think motorbikes: huge hp out of 1l: it idles at 1500 rpm and has to rev to 15k to do it and only makes 1/3 that number of ftlbs (similar ftlbs to the same motor with a low-rpm cam). My BMW is a great example: They took the 1150 motor, punched it out to 1200 and slapped smaller valves and cams, long intake runners, and a different tune to go from 100hp @ 8k to 63hp @ 6k while the torque stayed the same 70ish ftlbs but the peak moved from 6k to 3k. My bike tops out at 105mph from the factory but pulls like a turbodiesel at more moderate speeds.

 

That isn't saying there aren't gains to be had but don't expect much peak number gain, especially for the money, without raising the redline. As others have said though, unless you're making a fair bit of power over stock, you'll be fine.

Edited May 26, 2016 by kamesama980

[Mad Mechanic]

I'd rather not sacrifice my low end as that is where this engine would primarily be used, and I'm surely not building some 2.5L dyno queen.

 

So we have established that the 251 block is plenty fine for what I want to do, however I need to address issues like oiling, so where is oiling a problem on this engine and how do I improve that? (links to other threads welcomed).

 

Also, is there a way to move the torque band lower in the RPM range? According to wikipedia (I know it's not a great source of info but it's a start) peak torque for the 251 is found at 4400 rpm. Would I need to be looking at a set of camshafts?

 

As far as rods, should I stick with the stock cc length of 131.6 mm or look at 130.5mm cc length rods? (I suspect going to the shorter rods would lower my compression ratio and defeat the purpose of what I'm trying to do).

 

For ECU/EMS, I pulled the stock ECU/EMS with the engine, but from my reading I get the impression that was a fairly pointless thing to do (other than maybe trying to bench start the engine in stock form). My understanding is that the stock ECU/EMS from a 2003 outback is not tuneable. Could I pull a stock ECU/EMS from a later car that allows aftermarket tuning or just replace with an aftermarket unit like a Hal-Tech?

[matt167]

2004-2007 is tunable with rom raider. But limted

[kamesama980]

yea, the rom-raider tunable ECMs are for, it sounds like, the throttle-by-wire (nasty things anyway lol). ECM tuning without other mods won't make a huge difference unless the stock tune is bad for some reason. Yes, the biggest thing would be a set of RV cams or a custom cut (no I don't know where) or a smallish supercharger ($$, tuning, fab, etc). long-tube tri-Y header and not-too-big exhaust might help some but generally, exhaust doesn't net you much down low because it's already sized to (barely) flow enough up high.

 

I saw an Eaton M90 supercharger build on RS25.com that's pretty much my goal. Big fat bottom end torque for towing and auto-x.

[Mad Mechanic]

Pulling a later ECM poses two issues for me given my chosen motor (the EJ 251).

 

First is the lack of a drive-by-wire on the base motor. Now I might be able to get around this by transplanting a later intake manifold from the ECM donor car, but I do prefer an old-school throttle cable (personal preference).

 

Second is that I chose the 251 specifically for the MAP instead of MAF for calculating intake volume, when Subaru went to the 253/254/255/257, they all use a MAF. So again I would probably have to transplant the ECM donor car's instake manifold AND air intake system for the MAF sensor.

 

I've thought about a supercharger at times, there is additional cost (parts and fabrication) involved in going that route, but there are some advantages too. For one, it is a simpler system than a turbo, but the flip side of that is you don't (typically) see the "massive" power gains that turbo setups get. On the other hand, supercharger power tends to come on sooner as you aren't waiting for a turbo to spool.

 

Plus, who hasn't dreamed about a Mad Max style supercharger sticking through the hood. I have also thought that the Subaru intake manifold (or a custom one) would make a perfect platform for a roots blower, similar to a V-block engine.

 

As for camshafts, I've come across several options for those online, everything from aftermarket manufacturers that offer off-the-shelf ground cams for the SOHC engines to a couple custom cam grinders that allow you to specify what you want.

[WoodsWagon]

For ECU/EMS, I pulled the stock ECU/EMS with the engine, but from my reading I get the impression that was a fairly pointless thing to do (other than maybe trying to bench start the engine in stock form). My understanding is that the stock ECU/EMS from a 2003 outback is not tuneable. Could I pull a stock ECU/EMS from a later car that allows aftermarket tuning or just replace with an aftermarket unit like a Hal-Tech?

Go aftermarket. Stinger, Electromotive, MoTec, HalTech whatever flavor you prefer. They pull an extra 20hp+ out of the EJ25 with an aggressive tune. Premium fuel required at that point. Later on if you go forced induction it's easy to re-tune to match.

[Fairtax4me]

Delta cams are popular choice for the older 2.2 engines. Lots of people here run them, myself included.

 

I've thought the same about sticking a twin screw on top of a subaru manifold. Big pulley and a triple-flap bug catcher sticking out of the hood.

Wouldn't sound as cool as a big v8 though.

[Mad Mechanic]

So I hope I'm not past the time limit for resurrecting a thread, but I had a question about connecting rods.

 

My EJ251 has the "odd ball" 131.25mm connecting rods as opposed to the more common WRX/STi 130.50mm connecting rods. Now, I have a suspicion that Subaru put slightly longer con-rods in the EJ251 because it was never intended to be a Turbo motor, so this was a way to increase the compression ratio on an N/A motor.

 

But when I start in on the rebuild of this motor, bearing in mind I don't have intentions of forced induction (talk of supercharging aside for the time being), would there be a good reason to get a set of WRX/STi spec (130.50mm) rods? They are more commonly available. The biggest argument I could see against doing this would be a loss of compression ratio and therefore power.

 

Thoughts?

[Fairtax4me]

The longer rods would give you more compression, assuming you use the 251 pistons. With those rods the pistons would likely crest above the block deck, which would necessitate using a thicker head gasket.

[Mad Mechanic]

The longer rods would give you more compression, assuming you use the 251 pistons. With those rods the pistons would likely crest above the block deck, which would necessitate using a thicker head gasket.

 

I'm not sure I follow your statement. I agree that longer rods will give more compression, the longer rods being those for the 251, but your second part about needing a thicker head gasket if I use 251 rods and pistons. I'm starting with a complete 251 block, so wouldn't the block/heads already be setup to accommodate the longer rod/piston combo?